EP2726785B1 - Mixing device in a bypass steam line - Google Patents

Description

The invention relates to a mixing unit for mixing a flow medium with a cooling medium, comprising a tube channel portion to which a mixing section is fluidly coupled, wherein the mixing section comprises a plurality of Laval nozzles through which the flow medium can be flowed, wherein injection channels are formed in the Laval nozzles through which the Cooling medium flows in such a way that a mixing of the flow medium takes place with the cooling medium.

In steam power plants steam is generated in a steam generator, which converts the thermal energy of the steam into rotational energy in a turbine set coupled to the steam generator in terms of flow. The rotational energy is finally converted into electrical energy. As long as the steam power plant runs in continuous operation and the load on the electric generator is comparatively constant, the thermodynamic conditions are comparatively constant in time.

However, there are situations in which the steam power plant needs to be adapted to rapidly changing load situations. For example, it may be that a fault occurs and the generator suddenly has to be disconnected from the grid. It may also happen that the steam power plant has to switch unexpectedly from full load to partial load. Such load changes are a challenge to the control technology of the entire steam power plant. One way to follow or counteract rapidly changing load changes is that the steam generated by the steam generator, which flows in continuous operation or full load operation directly to the high-pressure turbine section, is led directly to the condenser via a bypass station. In this bypass station devices are provided which mix the highly heated steam with water, thus the thermodynamic To change ratios of the steam. This water is injected into the steam. This is done according to the prior art in a diverter, in which a Laval nozzle is arranged, the injection channels, is injected through the water into the steam.

However, it has been shown that this noise emission is relatively strong. Furthermore, it has been shown that the temperature distribution is not homogeneous enough, which leads to a non-optimal performance in partial load.

Essentially, diverter stations used today consist of a diverter valve and the diversion steam inlet. The bypass steam introduction includes an orifice, a water injection device, and a mixing tube. When starting the steam power plant or after a trip of the steam turbines accumulating steam is cooled by the Umleitstation by injecting water and introduced directly into the condenser.

It is an object of the invention to allow a better mixing of the water with the steam during operation and at the same time to reduce a noise emission.

This object is achieved by a mixing unit for mixing a flow medium according to claim 1.

In the dependent claims advantageous developments are given.

With the invention, the way is thus taken, contrary to the existing concept in which the steam flows through only a single aperture, to use multiple apertures. The disadvantage of the use of a single aperture is that the mixing is not optimal, especially at the edges of the mixing section. The use of multiple apertures results in better mixing and reduced noise emission.

An essential idea of the invention is that two Laval nozzles, which are adjacent to one another, are arranged offset to one another in the flow direction. To cool the steam, water is injected into the bypass steam line in the bypass mode. In order to achieve a good atomization of the water and thus an effective cooling, the steam is passed through a Laval nozzle or through a pinhole before mixing, whereby the flow rate greatly increased. Although the high relative velocity between steam and water drops leads to a good atomization, but has the disadvantage that the water droplets do not reach into the core of the vapor stream and thus the inner part or the inner core of the vapor stream is not sufficiently cooled. The Laval nozzles are now moved axially in the flow direction of the flow medium. When flowing through a Lävaldüse a sound wave is generated. The sound wave is created behind a Laval nozzle. If the Laval nozzle is additionally displaced axially by a length so that sound wave peaks and sound wave troughs from different and adjacent Laval nozzles cancel each other out, the overall sound emission is significantly reduced.

Thus, an essential feature here is that the individual Laval nozzles, which are arranged adjacent to each other, are axially mutually displaced.

The Laval nozzles are coupled with a displacement device, whereby a displacement of the Laval nozzles during operation is possible. Thus, it is proposed to form an active displacement, which can be done electrically or hydraulically or by other means so that the Laval nozzle planes are displaced relative to each other so that different frequency bands can be influenced during operation. Thus, a noise emission can be effectively reduced at different operating conditions.

In a first advantageous development, the Laval nozzles are made identical to one another. This leads to a better predictability of the sound wave troughs and sound wave peaks and it can thus be better determined beforehand by the sound emission by calculations in how far the axial displacement has to take place.

In a further advantageous embodiment, the Laval nozzles are coupled to a displacement device, wherein a displacement of the Laval nozzles during operation is possible. Thus, it is proposed to form an active displacement, which can be done electrically or hydraulically or by other means, so that the Laval nozzle planes are displaced relative to each other so that different frequency bands can be influenced during operation. Thus, a noise emission can be effectively reduced at different operating conditions.

Figur 1

eine Querschnittsansicht einer herkömmlichen Vermischeinheit;

Figur 2

eine Querschnittsansicht einer erfindungsgemäßen Vermischeinheit;

Figur 3

eine Querschnittsansicht eines Teils der Vermischeinheit.

The invention will now be explained in more detail with reference to an embodiment. Show it:

FIG. 1

a cross-sectional view of a conventional mixing unit;

FIG. 2

a cross-sectional view of a mixing unit according to the invention;

FIG. 3

a cross-sectional view of a part of the mixing unit.

FIG. 1 shows a mixing unit 1 according to the prior art. Such a mixing unit 1 is characterized by a tube channel section 2 in which a flow medium 3 flows in the direction of a mixing section 4. In this mixing section 4, a Laval nozzle 5 is arranged, in which the flow medium is accelerated. In the Laval nozzle 5 injection channels 6 are arranged, through which flows a cooling medium such as water. The cooling medium is mixed with the flow medium 3 in a pipe section 7, which is fluidically connected to the mixing unit 4.

FIG. 2 shows a representation according to the invention of the mixing unit 1. The difference to the mixing unit 1 according to FIG. 1 is that in the mixing section 4, a plurality of Laval nozzles 5a, 5b, 5c are arranged, through which the flow medium 3 flows and in each of which an injection channel 6 is formed, is mixed by the water with the flow medium. Furthermore, the difference between the mixing unit 1 exists FIG. 1 and FIG. 2 in that the Laval nozzles 5a, 5b, 5c in the flow medium direction 8, which can also be referred to as the axial direction, are shifted from one another. By this shift, the sound wave valleys, which coincide with sound wave mountains of the adjacent Laval nozzles, repealed. As a result, an overall noise emission reduction is achieved. The pipe section 7 is finally connected to a capacitor, not shown.

The axial displacement of the Laval nozzles 5a, 5b, 5c against each other can be effected by an active displacement by means of electrical or hydraulic forces. This can be done during operation, where different operating conditions occur. As a result, different frequency bands can be influenced, which also reduces overall noise emission during operation.

You can measure the frequency band during operation and then shift the aperture against each other so that the noise emission is minimal. It is possible to determine the most favorable axial positions for each load point in advance when commissioning the system, and then drive them in during operation alone, without having to actively measure the frequency spectrum.

FIG. 3 shows a representation of the displacement of the Laval nozzles 5a and 5b by way of example. The Laval nozzle 5a is shifted relative to the Laval nozzle 5b by the length L to each other. At a sound frequency of 1000 Hz, this would result in a sound velocity of about 500 m / s, resulting in a required length of 0.5 m. This length can be set statically to a first approximation or, as described above, also during operation by an active shift.

Claims (6)

1. Mixing unit (1) for mixing a flow medium (3) with a cooling medium,
   comprising a pipe conduit section (2), to which a mixing section (4) is coupled fluidically,
   Mixing section (4) comprising a plurality of Laval nozzles (5, 5a, 5b, ...), through which the flow medium (3) can flow,
   there being formed in the Laval nozzles (5, 5a, 5b, ...) injection ducts (6) through which the cooling medium flows in such a way that mixing of the flow medium (3) with the cooling medium takes place,
   Laval nozzles (5, 5a, 5b, ...) adjacent to one another being arranged so as to be offset in relation to one another in the direction of flow (8) of the flow medium (3),
   characterized in that
   the Laval nozzles (5, 5a, 5b, ...) are coupled to a displacement device,
   displacement of the Laval nozzles (5, 5a, 5b, ...) being possible during operation.
2. Mixing unit (1) according to Claim 1, the Laval nozzles (5, 5a, 5b, ...) being designed identically to one another.
3. Mixing unit (1) according to Claim 1 or 2, the injection ducts (6) being formed obliquely to the Laval nozzle wall.
4. Mixing unit (1) according to one of the preceding claims, the flow medium (3) being steam.
5. Mixing unit (1) according to one of the preceding claims, the cooling medium being water.
6. Mixing unit (1) according to Claim 1, displacement taking place by electrical or hydraulic means.

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